Ph.D Defense: Yuhao Wang

    Tuesday, May 13, 2014 - 2:00pm
    Meinel 747

    "Advanced Theory of Field Curvature"


    Classical field curvature theory emphasizes the Petzval theorem, which models field curvature aberration to the fourth order. However, modern lens designs use aspheric surfaces. These surfaces strongly induce higher order field curvature aberrations which are not accounted for Petzval field curvature. This dissertation focuses on developing higher-order field curvature theories that are applied to highly aspheric designs. Three new theories to control field curvature aberration are discussed. Theory 1: An aspheric surface that is close to the image and has two aspheric terms sharply reduces field curvature by 85 percent. Theory 2: An aspheric surface that is farther from the image plane induces astigmatism to balance Petzval field curvature. Theory 3: Oblique spherical aberration can be induced to balance Petzval field curvature. All three theories are applied to real design examples including the following lenses: cellular phone, wide-angle, fast photographic and zoom lenses. All of the analysis results are consistent with the theories. Moreover, two types of novel aspheric surfaces are proposed to control field curvature. Neither of the surfaces are polynomial-type surfaces. Examples show that the novel aspheric surfaces are equivalent to even aspheric surfaces with two aspheric coefficients in terms of field curvature correction. The study on field curvature correction using aspheric surfaces provides an alternative method to use when aspheres are accessible. Overall, this dissertation advances the theories of field curvature aberration, and it is particularly valuable to evaluate highly aspheric designs when Petzval theory is inapplicable.